The present invention relates to installation heads of the type installed in die presses to install self-piercing, self-clinching and self-riveting fasteners or fastening elements. More particularly, the installation head of this invention includes a means for cleaning the fastener sensor probe or switch, which is normally interconnected to the control of the die press, such that the die press is not actuated if a self-attaching element is not located ready for installation.
Self-attaching fasteners or fastening elements, such as pierce nuts, rivets, weld nuts, self-piercing studs and the like, are used today in many mass production applications, including automotive manufacturing. Pierce nuts and self-piercing studs are used by the automobile industry, for example, to interconnect various structural elements and to connect body panels to structural elements. Several such self-attaching fasteners may be attached to a structural element or a body panel at a time, generally in a die press. The die press may also be utilized to simultaneously form the structural element or body panel and install several self-attaching fasteners. A sheet of steel may be inserted in a die press, for example, which includes a plurality of installation heads. When the die press is closed to form a configured panel or structural element, the self-attaching fasteners are simultaneously installed in the panel or structural element by the installation heads.
In a typical application, one of the die shoes includes a plurality of installation heads which receive the self-attaching fasteners or fastening elements from a hopper or coiled reel and the opposite die shoe includes aligned die buttons. When the press is closed, the self-attaching fasteners are driven into the panel by a reciprocating plunger in the installation head to pierce the panel and the panel surrounding the pierced opening is simultaneously clinched to the seIf-attaching fasteners by the die buttons. Self-attaching fasteners may also be attached in pre-pierced panel openings by a similar process.
Because several operations may be performed simultaneously in the die press, as described, it is essential in such applications that means be provided to signal the presence of the self-attaching fasteners in the installation heads ready for installation. In a typical installation, a fastener sensor means, such as a proximity switch, is located in the installation head, which is interconnected electrically to the control panel of the die press. If the proximity switch senses that a self-attaching fastener or fastening element is not located in the installation head ready for installation, the die press cannot be actuated and a signal is normally provided to indicate which head requires servicing. Although such installation heads are normally rugged and relatively simple in operation, one or more of the installation heads may require service or the supply of self-attaching fastening elements may be exhausted. It is also possible for the self-attaching fastening elements to become jammed in the feed system, rendering the installation head temporarily inoperative.
If, however, the fastener sensor means becomes fouled with oil, burs, chips or other debris, the sensor means may indicate the presence of a self-attaching fastening element in the installation head ready for installation when no fastener is located beneath the plunger, ready for installation. When this happens, the installation head is cycled, but no fastening element is installed by the installation head. There is, therefore, a necessity for periodically cleaning the fastener sensor element. At present, this is accomplished by interrupting the operation of the die press and cleaning the windows of the proximity switches, as necessary based upon experience. The installation heads of the type described herein have been utilized to install pierce nuts as disclosed in U.S. Pat. Nos. 3,098,576, 3,718,965, 3,942,235, 3,946,478 and 3,961,408, all assigned to the assignee of the instant invention. U.S. Pat. No. 4,505,416 discloses a simplified pierce nut installation head, which is also assigned to the assignee of the present invention. U.S. Pat. No. 4,555,838 discloses an improved self-piercing stud and installation head and U.S. Pat. No. 4,610,072 discloses a round shoulder self-piercing nut and installation head, both of which are assigned to the assignee of the present invention. Self-clinching fasteners and installation heads are also used in mass production, wherein the fastener is installed in a pre-pierce panel opening, such as disclosed in U.S. Pat. No. 3,938,239. Further, self-riveting fastening elements may be installed by a similar installation head and installation heads are used in mass production to install weld nuts and the like. In mass production, a proximity switch or other sensor means is provided to indicate the presence of a self-attaching fastening element ready for installation prior to activating the installation head.
Various means have been tried to clean the fastening element sensor during installation. For example, a jet of air has been directed through the fastener inlet passage against the window of the proximity switch, which engages the proximity switch each time the plunger is retracted. This means of cleaning the proximity switch has not, however, proven sufficiently reliable, particularly in mass production applications where several operations are performed with each stroke of the die press, such as described above. The need therefore remains for a more reliable means of cleaning the self-attaching element sensor means, preferably during installation of the fastening elements and not requiring down time of the die press.